The present invention relates to pumps for pumping molten metal and, in particular, to devices used to prevent objects from entering the inlet and jamming such pumps.
Pumps used for pumping molten metal typically include a motor carried by a motor mount, a shaft connected to the motor at one end, and an impeller connected to the other end of the shaft. Such pumps also include a base that includes an impeller chamber. The impeller is rotatable in the impeller chamber. Support members extend between the motor mount and the base. An optional volute member may be disposed in the impeller chamber. Pumps are designed with shaft bearings, impeller bearings and bearings in the base to prevent the shaft or impeller from contacting the base, which could damage the shaft or impeller. The shaft, impeller and support members for molten metal pumps are immersed in molten metals, such as aluminum, magnesium, copper, iron and alloys formed from these metals. The pump components that contact the molten metal are composed of refractory material, for example, graphite or silicon carbide.
Pumps commonly used to pump molten metal may be in the form of a transfer pump having a top discharge or a circulation pump having a bottom discharge, as disclosed in the pump publication xe2x80x9cH.T.S. Pump Equation for the 80""sxe2x80x9d by High Temperature Systems, Inc., which is incorporated herein by reference in its entirety.
One problem that is often encountered with molten metal pumps is that they are damaged by solid impurities contained in the molten metal. The solid impurities include chunks of refractory brick and metal oxides, such as aluminum oxide. If a solid impurity becomes jammed between the impeller and the impeller chamber, the impeller or the shaft may be destroyed.
It is known in the art to place a plate above the inlet to the base of the pump to prevent some of the solid impurities from entering the base, thereby inhibiting jamming of the pump. U.S. Pat. No. 4,786,230 to Thut discloses a dual volute molten metal pump that includes a baffle plate above the inlet to the base of the pump for inhibiting chunks of material from entering the base of the pump. Pumps that include baffle plates are still subject to jamming, since relatively large solid impurities are still able to enter the opening of the base through a slot-like opening formed between the base and the baffle plate.
Filters have been designed to be placed over the inlet of a molten metal pump which are formed of a refractory with five pores that prevent all foreign material from entering the pump. These filters are cast, which limits their dimensional precision. Filters of this type are disclosed in U.S. Pat. Nos. 4,940,384; 5,078,572; and 5,286,163 to Amra et al. The Amra et al. patents disclose a molten metal pump that includes a filter that prevents ingestion of solid particles, as well as dross, in the molten metal. The filter has a low porosity, which requires the filter to have a large surface area to maintain a sufficient flow rate for the pump. Since the porosity of these types of filters is low, they tend to clog over time and, therefore, do not provide a workable solution.
It is known in the prior art to surround the shaft of the molten metal pump with a sleeve. The sleeve may include an opening that allows molten metal from the molten metal bath to enter the chamber of the molten metal pump. One example of this configuration is shown in FIG. 1 of U.S. Pat. No. 6,152,691 to Thut, which is incorporated herein by reference in its entirety.
The molten metal processing market demands a pump that does not jam, which would cause damage to the shaft and impeller of the pump. Accordingly, there is a need for a protected inlet for a molten metal pump that prevents the molten metal pump from jamming and avoids pump clogging.
The present invention concerns a protected inlet or guard for preventing jamming of a molten metal pump. The protected inlet or guard includes a flat surface and a wall that extends from the periphery of the flat surface. The flat surface includes a central opening that is sized to fit around the impeller shaft of the molten metal pump. The wall is sized to fit within an inlet opening of the pump. The wall includes openings through which molten metal can enter the inlet of the pump. The openings have a maximum dimension that is less than a specified distance from a wall of a pump chamber and greater than 0.250 inches.
In one embodiment, the flat surface is a circular plate and the wall is cylindrical. The guard may be constructed from a non-metallic, heat resistant material, such as a refractory material. The openings in the wall of the guard may be round and may have a diameter that is greater than or equal to xc2xcxe2x80x3. In one embodiment, the size of the openings is between xc2xcxe2x80x3 and ⅝xe2x80x3. In one embodiment, the protected inlet or guard is machined. Disposal in the circular plate is a bearing ring that extends around the pump shaft.
A pump constructed in accordance with the present invention that is less prone to jamming includes a motor, a shaft, an impeller, a base, an inlet opening, a base opening, and a discharge passage. One end of the shaft is connected to the motor. The impeller is connected to the other end of the shaft. The base includes a chamber in which the impeller is rotatable. The impeller is positioned a specified distance from a wall of the chamber. The inlet includes a plurality of openings through which molten metal can enter the base. The plurality of openings are defined by a maximum dimension that is less than the specified distance, but greater than 0.250 inches. The base opening is in either the upper or lower portion of the base and receives the impeller. The base opening is disposed adjacent to the inlet. The molten metal enters the inlet of the base and leaves the chamber through the discharge passage.
In one embodiment, the chamber defined in the base is a spiral-shaped volute opening around the impeller which increases in size in a circumferential direction toward the discharge passage. In one embodiment, the pump includes a volute insert that is positioned within the chamber. In this embodiment, the specified distance is less than the minimum distance between the impeller and a wall of the chamber and less than the minimum distance between the impeller and the volute insert. In one embodiment, the impeller is positioned in the chamber so as to form a volute-shaped volume between the impeller and the chamber.
To pump molten metal with the pump of the present invention, the base is submerged in a bath of molten metal. The impeller on the end of the shaft is rotated in the chamber of the base. The rotation of the impeller causes molten metal to be drawn into the chamber through the plurality of openings that define the inlet of the pump. Large solid particles that are larger than the minimum distance are engaged by the inlet to prevent the large solid particles from entering the pump chamber. Small particles are drawn through the plurality of openings of the inlet into the pump chamber. Molten metal is passed through the outlet of the base. In one embodiment, the large particles engaged by the pump inlet are silicon particles.
Molten metal that is used for engine blocks, pistons and other related engine components now require increased silicon in the composition. The silicon is typically added in the form of pieces of about 3xe2x80x3 by 5xe2x80x3 in size. It takes a certain amount of time before the silicon pieces dissolve, much like dissolving sugar cubes, as opposed to granulated sugar, in coffee. The chunks of metallic silicon are brought into the base of the pump where they easily find their way around the opening formed by typical baffle plates, thereby resulting in jamming and destruction of pump components.
A pump constructed with the guard of the present invention prevents silicon pieces that are large enough to damage the pump from entering the inlet of the pump, thereby preventing jamming and destruction of the pump. When silicon is the cause of jamming of a pump, it is likely that the cause of the jam will not be discovered, because the silicon dissolves after the pump jams. Inspection of the pump would not reveal that silicon chunks were the cause of the jam.
The guard of the present invention effectively avoids jamming of the pump. Since the openings of the guard are much larger than typical filters, efficiency of the pump is enhanced. The improved efficiency produces a more homogeneous blend of molten metal and allows the temperature of the molten metal to be better maintained. Since the guard of the present invention can be machined to a great precision, it may include a bearing ring. The present invention also reduces the temperature of exhaust gases that are discharged by the pump of the present invention as a result of more efficient pumping.
Many additional features, advantages and a fuller understanding of the invention will be had from the accompanying drawings and detailed description that follows. It should be understood that the above summary of the invention describes the invention in broad terms, while the following detailed description of the preferred embodiments describes the invention more narrowly and presents preferred embodiments which should not be construed as necessary limitations of the broad invention as defined in the claims.